[Music] many molecules studied in biology are based on carbon the chemical properties of the carbon atom allow it to form many diverse structures with a range of functions carbon is the sixth element on the periodic table with six protons and six electrons and four of the six electrons are in the outermost electron shell called veence electrons one of the most important chemical properties of a carbon atom is its ability to form four coal bonds with other atoms because of the arrangement of its four veence electrons a calent bond is formed by the sharing of valence electrons between two adjacent atoms coal bonds are the strongest type of bond between atoms and therefore carbon-based molecules are very stable carbon atoms can form calent bonds with with other carbon atoms or with atoms of other elements such as hydrogen oxygen nitrogen and phosphorus it can form four single calent bonds with one other element as it does in methane CH4 or include double calent bonds as found in carbon dioxide CO2 carbon atoms can also link up by calent bonds to form a chain of any length like in fatty acids or a ring containing carbon and nitrogen like in the nitrogenous base thyine carbon's ability to form four calent bonds allows for a large range of simple to complex molecules to be formed making it a great building block for all living things macro molecules are molecules composed of a very large number of atoms the large complex molecule is often referred to as a polymer composed of smaller subunits called monomers the main classes of macromolecules referenced in IB Biology are primarily carbon compounds such as polysaccharide which are sugars polypeptides which are proteins lipids and nucleic acids each of these is made by linking respective subunits monosaccharides amino acids and nucleotides via condensation reactions in a condensation reaction two molecules are linked together and in the process a smaller molecule water is released this happens by removing a hydroxy group O from one molecule and a single hydrogen atom H from the other molecule creating H2O a bond is then formed to connect the two molecules where the atoms to make the water were removed energy is required to construct polymers by condensation reactions and is supplied by adenosine triphosphate or ATP for the IB exam you need to know how these condensation reactions are used to build all four macromolecules we covered nucleic acids in section a1.2 we will cover polysac aides and lipids in more detail in this video and polypeptides will be covered in section B 1.2 just as we can build up large macromolecule structures via condensation reactions we can also do the opposite to break them down this would mean taking the large chain polymers and breaking them apart into their individual subunits or monomers this type of reaction is called hydrolysis and works in opposition to condensation recall that the condensation reaction used to build longchain polymers has molecules bind via the creation or condensing of a water molecule to undo this reaction via hydrolysis a water molecule can be split and the subsequent hydrogen and hydroxy group can be reformed on the original monomers thus Breaking the Bond that linked them together this makes sense when breaking down the name hydrolysis the suffix lysis means to break down and the prefix Hydro means water so we can translate the literal meaning of the word as to break apart with water and this is exactly what we see a polymer being broken down back into separate monomers via a water molecule now in this video we will cover carbohydrates and lipids and we will begin with carbohydrates when you hear this term carbohydrate the first thing that should pop into your head is sugar because carbohydrates are nothing more than sugar molecules either seen individually or linked together in a chain the basic subunit of a carbohydrate is a monosaccharide mono prefix meaning one and saccharide suffix relating to Sugar these structures are built using only three different atoms which are carbon hydrogen and oxygen and have them in specific ratios glucose for example is a monosaccharide or a single sugar it contains six carbon atoms 12 hydrogen atoms and six oxygen atoms so we notate the chemical formula for glucose as C6 h126 now the ratio rule for carbohydrates is that for every carbon you have there are the same amount of oxygen atoms and twice as many hydrogen atoms so we can say the ratio is one to 2: one with carbon hydrogen and oxygen monosaccharides can come into shapes which we call ring structures and straight chain form so if we look at glucose here we can see this is the ring structure and this is the straight chain form both versions carry the same chemical formula along with the structural representation you also need to be able to identify different types of monosaccharides that we call pentoses and hexoses pentoses contain five carbon atoms as seen here with ribos and hexoses have a six carbon structure like we see in glucose in any case both of the molecules keep the ratio of carbon to hydrogen to oxygen like glucose with C6 h126 and ribos having the chemical formula C5 h105 you can see that the ring structure is different with ribos having five points to the central ring where glucose has six but the ring structure is not a defining characteristic of labeling it as pentos or hexos it solely depends on the number of carbons in addition to structures you need to know a few properties of monosaccharides and specifically glucose because it is a very important sugar structure for living things first monosaccharides including glucose are small and soluble in water which means they can easily be transported in living tissue because living tissue is based around water second the oxidation of this molecule which describes how electrons can be transferred from the molecule within a chemical reaction can yield a great amount of energy for cells which we see in the process of cellular respiration ation but more on that in another video so for now just know that monosaccharides like glucose can be used as a quick energy source for living things lastly glucose and many carbohydrates are very stable molecules which make them great candidates for energy storage which we will talk more about on the next slide be sure to memorize all of these Key properties of glucose for the IB exam a monosaccharide is a single sugar molecule and if we connect two of them we call it a disaccharide prefix die meaning two and if we continue to connect sugar molecules to make a longer chain we call it a polysaccharide the prefix poly meaning many or more than two there are three broad categories of these large carbohydrate molecules that you need to know about which are starch glycogen and cellulose starch and cellulose are only made in Plants while glycogen is made in animals and looking at a few structural differences we can see that cellulose structures are unbranched starch structures are moderately branched and glycogen is heavily branched and if we look at the similarities between these molecules we can see that all of them are made out of the same repeated structure glucose before we talk more about these large molecules let's learn a bit more about the structure of glucose we know that glucose is a single sugar molecule that has the chemical formula C6 h126 and commonly but not exclusively takes on the shape of a hexagon so if we look at a drawing of its structure we should be able to account for all of these atoms we start naming carbons from the carbon on the rightmost point which we call carbon number one we circle around moving clockwise to count the other carbons but notice that carbon number six is not part of the hexagon structure it branches up and off of carbon 5 which leaves the sixth point of the hexagon occupied by an oxygen atom in most drawings within organic chemistry assume that that any corner or point where two lines meet is a carbon if it is not otherwise labeled next we can count the oxygen atoms and we can see that there are six total finally we should have 12 hydrogen atoms all of them are shown here but know that on some structures if nothing is shown to give carbons the four bonds it makes we should always assume that a hydrogen is present to get it to make four bonds okay so back to glucose all of the atoms within our chemical formula are accounted for now the last thing we need to know about glucose which is very important is that it comes in two different ring forms which are called Alpha and beta there is one very specific difference that exists between these forms take a second to see if you can spot it if you notice a difference between the orientation of the bonds coming off of the first carbon you got it right in alpha glucose the O group is oriented down and in beta glucose the O group is oriented up and again this only applies to the hydroxy group off of the first carbon you can see that Carbon 2 is always down carbon 3 is up and carbon 4 is down an easy way to remember this is that beta follows the up down up down pattern while Alpha follows the down down up down pattern for the O groups let's take a look back at our larger polysaccharides to see why these structural components are important starting with starch we can see that the chain of glucose molecule contains glycosidic bonds that connect carbon 1 of one molecule to carbon 4 of another molecule we call this a one4 glycosidic bond if you look closely you can see that all of the oxygen atoms on the one and four bonds are pointed down and all glucose molecules are oriented this way this tells us that starch molecules only contain alpha glucose which is very important to remember only alpha glucose not beta glucose we can break this down further into different types of starch molecules based on if the structure is linear or branched if we only have one4 bonds between alpha glucose meaning the molecule is one straight line of sugars we call this amose but we can see here that sometimes the structure branches and this Branch shows a bond between carbon 1 of one molecule and carbon 6 of another and you guessed it we call this a one6 glycosidic bond if that happens and new chains of alpha glucose Branch off an existing chain it is no longer called amose and instead called Amal optin which is a combination of 14 and 1 six bonds next up we have glycogen which is similar in structure to Amal optin but it tends to Branch more and is created inside the body of an animal this structure because it branches also contains a combination of 14 and six glycosidic Bonds in addition you should be able to deduce that only alpha glucose is used to create this structure not not beta glucose both glycogen and Amal optin are very large molecules that can store large amounts of energy in plants and animals respectively their large structures make them less soluble in water compared to single monosaccharides which is good for being kept as storage but when the time comes hydrolysis can break glucose molecules off of the chain which can be moved to cells where energy is needed which was the point of storing it in the first place finally we come back to cellulose now the cell ose you can see is very different in structure because it is made up of beta glucose only because the O group on the carbon 1 in beta glucose is up and the o on carbon 4 is down when these beta glucose molecules join together every other molecule has to be inverted which we can see here as we count carbons counterclockwise every other one is upside down this makes the cellulose structure unique for many different reasons one of which is being able bble to form microfibrils that have extremely strong tensile strength these are the basis of plant cell walls and give plants their firm sturdy structure to stand upright and not burst under high amounts of internal pressure all because of the beta glucose produced structure and as always for the IB exam make sure you know the differences between all of these longchain polysaccharides while carbohydrates can create many large structures on their own they also have the ability to B with other macro molecules one example of this is a glyco protein which can be found on cell membranes the term glyco is in reference to the sugar part of the molecule and the protein part speaks for itself embedded within the phospholipids of the cell membrane we can find these glycoproteins which contain a short chain of monosaccharides that we call an oligosaccharide cells can read these chains on other cells in the process of cell recognition which is important for cells in multicellular organisms to be able to identify other body tissue from foreign cells or pathogens a specific example of this can be seen in our red blood cells and the determination of the AO blood groups as humans we have four different possible blood types which are a b ab and O these blood type combinations are made by different oligosaccharide chains which are called a b and O the base of these chains are identical with a having an additional n acetyl galactosamine and B having an additional galactose the purpose of these glycoproteins on red blood cells are to signify if foreign blood has entered the body so if you had blood type A and received a blood transfusion from type B blood your body would reject the blood and it could clot type O blood is unique because it does not cause any rejection problems as it has the same base structure of the other two just without the determining last sugar molecule our body will not recognize it as foreign and therefore not reject it we will cover the workings of ablo blood types in more detail in another video moving away from carbohydrate molecules let's now spend some time focused on lipids another large Macro Molecule found in the human body lipids are made out of carbon hydrogen and oxygen but do not follow any specific ratio like carbohydrates do general property that we need to know about lipids before we take a look at their structure is that lipids are generally hydrophobic this allows them to easily dissolve in non-polar Solutions but not in polar solvents like the water that makes up most of our body so we have different methods of transporting them some commonly occurring lipids that you should know are fats oils waxes and steroids let's take a look at the structure of lipids in more detail the main structure of most lipids are called fatty acids each fatty acid molecule starts with a carboxy group which has a carbon atom that is attached to an oxygen with a double bond and another oxygen with a single bond that is also attached to a hydrogen which we call a hydroxy group this is often written as Co from there a fatty acid then has additional carbons attached to the first carbon how many carbons should there be that depends on the type of fatty acid some have many carbons and are quite long While others are on the shorter side and only have a few there are two important lipid structures that are created with fatty acid chains that you need to know of which are triglycerides and phospholipids both of these start with a glycerol Group which has the chemical formula C3 h803 to make a triglyceride three separate fatty acid chains undergo condensation reactions with the open hydroxy groups on the glycerol resulting in a final triglyceride structure that looks like this the creation of the phospholipid is the same except one of the fatty acid chains is replaced with a phosphate group both of these molecules are core lipids seen in the body make sure to know their structures as they will pop up many times throughout the IB Biology curriculum taking a closer look at a fatty acid chain you will notice that each carbon within the fatty acid chain has a hydrogen molecule attached to complete all four bonds that carbon can make if there is a single Bond formed between each carbon in the fatty acid chain we call that a saturated fatty acid you can think about it being saturated with hydrogen because single bonds means more open spots for hydrogen atoms to bond to the valence electrons that each carbon atom has if there are any double bonds between carbon atoms we call this an unsaturated fatty acid monounsaturated would have just one double bond in the chain where polyunsaturated would have more than one this double bond can create a bend in the molecule which is not shown in this image it's actually shown in this one and also contain contains less hydrogen atoms because carbon can only make four bonds each double bond counting as two for both of the attached carbon atoms when we take a closer look at unsaturated fatty acids we can distinguish between two different isomers or types based on where the hydrogen atoms are in relation to the carbons that share a double bond if both hydrogens are oriented in the same direction as they are in this image we call this a CIS fatty acid CIS sounds like sisters that are close to each other and have a good relationship which is one way you can remember it notice how this impacts the shape of the chain causing it to bend if the two hydrogen atoms are oriented in different directions or facing opposite sides of the molecule it is called a trans fatty acid this does not have the same impact on the shape of the chain compared to the Cy isomer as seen here and results in a straight chained fatty acid lipids that contain straight chain fatty acid Tails tend to have higher melting points because they can be packed tightly together an example of this would be butter which is solid at room temperature if lipids contain many Cy double bonds and have bent fatty acids they tend to have a lower melting point and are liquid at room temperature like oil this is because they can't sit neatly and packed together next to each other because of the bent fatty acid chains when talking about lipids which are fats we have to mention the type of fat that humans carry in their bodies body fat is a necessity for survival because it holds important energy reserves that the body can use as needed the fat tissue that we have in our bodies is a specific type of tissue called atopos tissue which are basically cells that are stuffed with triglycerides triglyceride molecules are well suited for long-term energy storage because they are chemically stable hydrophobic and can store much more energy than a carbohydrate per gram in addition to that triglycerides are poor heat conductors which means they can help animals hold in body heat to stay warm and act as an insulator to combat cold weather they are also liquid at room temperature which makes clusters of atopos cells shock absorbent which is a reason we find a lot of fat tissue around our kidneys for protection hydrophilic molecules are polar and attracted to water because water is also polar hydrophobic molecules are non-polar and therefore not attracted to water and more attracted to other non-polar molecules phospholipids are unique because they contain parts that are both hydrophilic and hydrophobic if a molecule contains both of these properties we call it amphipathic because of this property when phospholipids are placed in water the heads of the molecules which are hydrophilic are attracted to the water and the Tails which are hydrophobic repel the water this naturally creates a formation where the Tails of the phospholipids will be next to each other because they are then away from the water which creates a unique double membrane structure this leaves the hydrophilic heads of the phospholipids coming in contact with water molecules which is preferred this double membrane structure called a lipid bilayer is what cell membranes are made of and more on that in other videos steroids are lipid molecules that have a unique structure which differ greatly from the usual fatty acid chain lipids we are used to seeing The Telltale sign that you are looking at a steroid molecule is that you see four carbon-based rings that are fused together which consist of three cyclohexane rings and one cyclopentane ring you can see examples here with testosterone and estradiol steroids have 17 total carbon atoms within their ring structures and can have additional carbons branching off the Rings as well because these molecules are mainly made out of carbon and hydrogen they tend to be hydrophobic this allows them to be able to pass through a lipid by layer and even stay within the by layer which as we discussed on the last slide has the hydrophobic core region where the fatty acid tails of the phospholipids come together make sure to remember this structural form of steroids because you will have to identify this General structure on the IB [Music] exam [Music]